Spatiotemporal variation in leafminer population structure and adaptation to individual oak trees

Stilbosis quadricustatella leafminers are microlepidopteran specialists of sand-live oak (Quercus geminata). These tiny moths produce one generation p er year and have a parasitic life-cycle and long larval stage that develops entirely within la single oak leaf. Differences in host-plant age, phenoty pe, and phenology generate a coarse-grained, spatially heterogeneous enviro nment for the leafminer population. Previous reciprocal transfers of leafmi ner eggs among mature oaks revealed that S. quadricustatella are locally ad apted to individual oak trees. In this paper we use genetic markers and an extinction-recolonization experiment to explore further variation in leafmi ner population structure. Allozyme loci indicate significant interdemic gen etic structure among recent colonists of new host trees, which weakens in t he 10th generation and disappears by the 40th generation. In contrast,adapt ive demic structure is evident by the 10th generation and is strong in the 40th generation, despite the potential for substantial intertree dispersal. We propose that host heterogeneity combined with leafminer fidelity to nat al trees promotes divergent selection and rapid demic evolution on individu al oaks, despite potentially high gene flow between the leafminers inhabiti ng them.